By Daniel Flynn and Dina Kyriakidou
ATHENS (Reuters) - Thousands of rock-throwing youths staged running battles with police in central Athens Monday in a third day of demonstrations at the police killing of a teenage boy which has unleashed anger at economic hardships.
Tear gas filled Syntagma square outside Greece's parliament as police clashed with left-wing demonstrators, beating some with batons and detaining others. Protests were reported in more than 10 cities across the nation of 11 million people, including Thessaloniki and the tourist islands of Crete and Corfu.
More than 130 shops have already been destroyed in the capital, crushing retailers' hope that Christmas would compensate for Greece's darkening economic outlook. Police have detained 35 people in Athens.
With a 24-hour general strike due Wednesday against economic reforms, analysts said Greece's worst riots in decades looked set to continue and could threaten the conservative government, which has a one-seat parliamentary majority.
"Enough with this government, which doesn't understand the problems of this country," said George Papandreou, leader of socialist PASOK opposition party.
The socialists already held a strong lead in opinion polls before the riots, benefiting from disenchantment at the ruling New Democracy party's privatisations and pension reforms. Political analysts say an early election could be called next year.
Anger at the killing of 15-year-old Alexandros Grigoropoulos by a policeman Saturday has even reached Greeks living overseas, who staged protests in London and Berlin.
As night fell on the Greek capital, thousands marched arm-in-arm through the city's main streets. Anarchists smashed car windows and chanted "Cops, Pigs, Murders." Some threw fire bombs at police and, for a third night, businesses burnt and explosions rang out.
"Police have lost control. The dead kid was only an excuse. It seems the police are not on the side of the people, that's why people support the youths," said Alexandros, a teacher who declined to give his second name.
WORST RIOTS FOR DECADES
The shooting angered Greek youths, resentful at a widening gap between rich and poor, made worse by the global credit crisis. Violence at student rallies and fire bomb attacks by anarchists are common, especially in Athens' Exarchia district where the boy was shot.
More than a dozen police stations in Athens were damaged by demonstrators, who also raided a small pro-government newspaper and broke into a weapons shop, emerging with ninja swords and knives. Hundreds of students occupied university buildings, playing cat-and-mouse with police who are forbidden to enter.
More than 50 people have been injured nationwide and millions of euros of property damaged. TV images showed one car parking lot in the Piraeus port where nine cars had been flipped on their roofs.
Prime Minister Costas Karamanlis expressed sorrow for the family of the dead boy but warned demonstrators to stop. The government would try to compensate property owners, he said.
"We will not tolerate unacceptable and dangerous events prompted by the tragic incident," he said Monday, in his first public appearance since the riots began.
Thessaloniki also saw street battles between police and hundreds of protesters, who smashed shops and threw rocks at government offices. Clashes took place in Crete and Corfu as well as the cities of Volos, Komotini and Chania.
"If this continues, it could have a devastating effect on the government and on stability," said Anthony Livanios of pollster Alpha Metrics.
Two police officers have been charged over the shooting -- one with murder and the other as an accomplice. A police statement said one officer fired three shots after their car was attacked by 30 youths in Exarchia.
A police official said the officer had described firing warning shots, but witnesses told TV he took aim at the boy. A coroner's report Monday said it was not possible to be sure.